The present invention relates to the manufacture of intraocular lenses (IOLs) for implantation in an eye. The present invention more particularly relates to a method of providing a protective mask for removable attachment to selected areas of an IOL during polishing of the IOL.
IOLs require highly polished surfaces free of surface irregularities. This is because the IOL is in direct contact with delicate eye tissues and any rough or non-smooth surface on an IOL may cause irritation or abrading of tissue or other similar trauma to the eye. It has been found that even small irregularities can cause irritation to delicate eye tissues.
IOLs are typically either molded or lathe cut. Subsequent to either of these operations, the IOLs usually have irregular or roughened surfaces that need to be smoothed. It is thus usually necessary to polish the IOL to smooth out any rough areas on the IOL. One known polishing method is tumble polishing wherein a batch of IOLs are placed in a tumbler for several hours with a polishing agent. Examples of tumble polishing IOLs may be seen in the following patents:
U.S. Pat. No. 5,133,159 discloses a method of tumble polishing silicone articles in a receptacle charged with a mixture of non-abrasive polishing beads and a solvent which is agitated to remove surface irregularities from the articles.
U.S. Pat. No. 5,571,558 discloses a tumbling process for removing flash from a molded IOL by applying a layer of aluminum oxide on a plurality of beads, placing the coated beads, alcohol, water and silicone IOLs in a container and tumbling the same to remove flash.
U.S. Pat. No. 5,725,811 discloses a process for removing flash from molded IOLs including tumbling the IOLs in a tumbling media of 0.5 mm diameter glass beads and 1.0 mm diameter glass beads, alcohol and water.
In recent years, IOLs have been purposely designed with sharp posterior edges which has been found to inhibit the unwanted growth of lens epithelial cells (LECs) between the IOL and posterior capsular bag, also known as posterior capsule opacification or xe2x80x9cPCOxe2x80x9d to those skilled in the art. One such method for creating a sharp posterior edge in an IOL is described in copending application Ser. No. 10/403,989 filed on Mar. 31, 2003 and of common ownership with the present application, the entire disclosure of which is incorporated herein by reference. Creating a sharp, discontinuous bend in the posterior capsule wall is widely recognized by those skilled in the art as an effective method for minimizing PCO. See, for example, Posterior Capsule Opacification by Nishi, Journal of Cataract and Refractive Surgery, Vol. 25, January 1999. This discontinuous bend in the posterior capsule wall can be created using an IOL having a posterior edge which forms a sharp edge with the peripheral wall of the IOL.
Thus, while polishing is a necessary step in the IOL manufacturing process to remove surface irregularities, a purposely formed, sharp, posterior edge is one area of the IOL which should not be polished. If this area of the IOL is not masked from the polishing operation, the sharp posterior edge will become rounded and not function to inhibit PCO as intended. There thus remains a need for a method for polishing IOLs having sharp posterior edges wherein selected areas of the IOL, namely the sharp posterior edge, is protected from the rounding effect of the polishing operation.
The present invention addresses the problem of protecting the sharp posterior edge of an IOL during the polishing operation by providing a removable mask for attaching to a respective IOL prior to subjecting the IOL to polishing. The mask is configured to cover only the sharp peripheral edge of the IOL such that only this selected area of the IOL is not polished during the polishing operation. In a preferred embodiment, the mask is made of an elastomeric material which can stretch to alternately insert and remove an IOL therefrom in a manner which will not harm the delicate IOL. The elastomeric material absorbs the force of the polishing action and thus protects the sharp posterior edge from becoming rounded during the polishing operation.